Decontamination of sub-systems of LWR plants has now become relatively common in the United States, and is widely recognized as a useful contributor to the reduction of radiation exposure of workers at these plants. Sub-system decontamination involves exposing a part of the reactor circuit to chemical solutions which dissolve the radioactive deposits which have built up on process equipment, including piping. The spent decontamination solutions are then treated by ion exchange to retain all of the chemical and radioactive burden of the solution on the resin, while clean water is returned to the system. LOMI is one example of a sub-system decontamination process having these characteristics.
The ion exchange resin carrying the radioactive burden is normally managed by dewatering or solidification of the resin in cement based matrices, for shipment off-site to an appropriate burial location. Since ion exchange resins have a limited capacity for radioactivity and chemicals, a majority of material sent for off-site disposal and burial is the ion exchange resin itself and its binding matrix rather than the radioactive waste materials which the ion exchange was intended to remove. It is therefore desirable to have a waste treatment process which will isolate the radioactive burden in a more concentrated solid matrix than the ion exchange resin presently in use.
The chemicals used in the decontamination processes are normally used in a "once-through" manner, i.e., the chemical is added to the decontamination circuit and is subsequently removed along with the radioactive burden on ion exchange resins. The chemicals are not altered or consumed to any significant extent during decontamination. It would therefore be desirable to use, recover and reuse chemicals for several decontaminations.